Cross Posts Between Sites

I’m setting up a network of sites that are related to the region where my client does business and I want the different sites to have content that is related to a specific part of the region (e.g. a town or a lake). Since there is overlap, some of the pages and posts will make sense for more than one site, but not necessarily all of them.

I’ve seen that there are some WPMU plugins which do some of the work for this to happen, but I was wondering if there is something that, rather than copying the entries, just creates a link to them. I’m thinking of something similar to a hard link in UNIX/Linux file system for those who understand how they work. To each site it would seem that the post or page is “theirs”.